1. Field of the Invention
The present invention relates to a method and apparatus for link adaptive multicast/broadcast transmission and reception, and more particularly, to a method and apparatus for efficient delivery of multicast/broadcast data in a wireless network.
2. Description of the Related Art
A multicast/broadcast transmission method in a wireless communication system is a method of simultaneously transmitting multimedia data such as audio or video data to a plurality of receivers through a common channel, and also is an efficient method of simultaneously transmitting multimedia data to a plurality of users.
Well-known examples of the multicast/broadcast transmission method include a multimedia broadcast and multicast service (MBMS) method in 3rd-generation partnership project (3GPP) universal mobile telecommunications systems (UMTS) and long term evolution (LTE) networks, a broadcast multicast service (BCMCS) method in 3rd-generation partnership project 2 (3GPP2) code division multiple access (CDMA) 2000 networks, a multicast broadcast service (MBS) method in worldwide interoperability for microwave access (WiMAX) networks, and a broadcast and multicast transmission method in IEEE 802.11 wireless local area networks (LANs).
In a conventional multicast/broadcast transmission method in a wireless network (3GPP UMTS, IEEE 802.11), unidirectional transmission is made from a transmitter (base station, access point (AP)) to a receiver (terminal, mobile station, user device). Due to the unidirectional transmission, the receiver cannot notify the transmitter about whether data is successfully received or not.
The performance of this conventional multicast/broadcast transmission method can be improved by improving the reception quality of a subscriber terminal located where reception quality is poor (for example, a cell border). For example, a transmission diversity technique and a multiple base station transmission technique may be used.
In order to satisfy service quality desired by subscriber terminals that receive a service, a feedback channel is requested between receivers and a base station. In order words, a feedback channel for reporting the reception status of multicast/broadcast data from a terminal, i.e., a receiver, to a base station is requested.
As such, in a new wireless system standard, a method of allocating an uplink (reverse link) channel for reporting reception quality from a terminal to a base station and adaptively transmitting data from the base station based on the reported reception quality is being researched.
First, in a 3GPP LTE network method, a base station transmits MBMS data only when a terminal in a cell area requests a predetermined MBMS service and the number of service-requesting receivers is detected whenever an MBMS service is provided.
As a base station allocates a different code signal with respect to each MBMS service and a terminal transmits to the base station a different code signal with respect to each requested service, the base station may detect whether a service-requesting terminal exists and the number of service-requesting terminals with respect to each service.
Second, in a multicast/broadcast data service group method, terminals notify a base station about a reception status of each data block and if a terminal does not receive a predetermined data block, the base station retransmits the data block to the terminal.
For this, the base station allocates an uplink resource block related to each downlink data block for transmitting multicast/broadcast data.
Terminals that do not receive a data block transmit to the base station a reception failure of the downlink data block, i.e., a negative acknowledgement (NACK) message, included in the allocated uplink resource block.
If a NACK message is received from a terminal, the base station retransmits a corresponding transmission data block to the terminal. If the number of terminals that transmit NACK messages is known, the base station retransmits a transmission data block having a large number of NACK messages from terminals with priority.
As described above, a multicast/broadcast service method in a wireless network includes a method of reporting a data reception status of a service receiving group to a base station and retransmitting data from the base station to terminals according to the report.
A method of reporting the channel status or the channel quality from each receiver in a receiving group to a transmitter and performing adaptive modulation or adaptive controlling of the date rate or transmission power by using the transmitter based on the reported quality has not yet been suggested.
However, an example of an adaptive multicast data transmission method in a wireless LAN environment includes a method of determining a data rate by using a transmitter based on the minimum value of a signal-to-noise ratio (SNR) of receivers in a receiving group.
In this method, the data rate of multicast data is varied according to a carrier sensing multiple access/collision avoidance (CSMA/CA) protocol, an AP broadcasts a multicast probing channel, terminals in a multicast receiving group measure a reception SNR through the probing channel, and terminals having a low reception SNR respond faster than terminals having a relatively higher SNR.
The fastest responding terminal becomes a leader of the multicast receiving group, a transmitter determines a transmission data rate based on the SNR of the leader, and only the leader transmits a data reception failure message, i.e., a NACK message to the transmitter.
The above-described conventional method can prevent collision between terminals and satisfy service quality to a certain degree by allowing a terminal having the lowest SNR to report reception SNR and to transmit a NACK message.
However, if two terminals have similar reception SNRs, pieces of channel quality feedback information may collide with each other and non-leader terminals may not transmit a NACK message. Thus, if an SNR of a non-leader terminal suddenly deteriorates or an error occurs in receiving data, the service quality of a corresponding terminal cannot be satisfied.
Also, since this method is based on a CSMA/CA protocol, resource reservation or allocation for data transmission is not efficient.